Connects to host <host> on port <port> with account <user> and password <pass>

The notification-handler must be #f if no notifications from the server are handled, otherwise the notification handler must be a function of one argument. The server can send notifications to clients. They depend on the server. The client can handle these notifications using the given notification handler.

The pass-hasher is a function that is called with a password and a chalenge. The function must be used to hash the password and the chalenge together.

This function tries to login right away. If the login fails, rpc-valid? will return #f.

The result of rpc-connect is a handle. rpc-valid? returns #t, if the handle is valid, #f otherwise.